Protector for electricity supply circuit

1. A protector for an electricity supply circuit including a power line, the protector installed on a vehicle to monitor a temperature of the power line connected to a load and configured to disconnect the electricity supply circuit when the temperature of the power line exceeds a preset threshold temperature, the protector comprising: a power switch configured to switch between connection and disconnection of the electricity supply circuit to the load; a controller configured to output a switching command signal to the power switch in accordance with an input signal from an operation switch; and a current detector configured to detect current flowing to the power line, wherein the controller comprises: a temperature estimation unit configured to estimate temperature increase of the power line based on the current detected by the current detector and conducting time when the electricity supply circuit is connected to the load, estimate temperature decrease of the power line based on an elapsed time when the electricity supply circuit is disconnected from the load by the controller, and estimate a temperature of the power line based on the temperature increase and the temperature decrease; a timer configured to count an elapsed time after the disconnection of the electricity supply circuit from the load by the power switch; a lower limit threshold determination unit configured to determine that the estimated temperature of the power line estimated by the temperature estimation unit has dropped below a predetermined temperature determined by an ambient temperature of the power line; and a mode switching unit configured to switch the controller to a low power consumption mode in which power consumption of the controller is lower than the power consumption in a normal operation mode of the controller, in response to the elapsed time counted by the timer being greater than a predetermined time and the lower limit threshold determination unit determining that the estimated temperature of the power line estimated by the temperature estimation unit drops below the predetermined temperature, wherein at least a part of the power line is heated by high temperature air from an engine in an engine room of the vehicle, and the predetermined time is determined based on the temperature increase of the power line by the high temperature air when forced air cooling operation of the engine room is stopped during the disconnection of the power switch.

2. The protector for the electricity supply circuit according to claim 1 , wherein the temperature estimation unit does not estimate the temperature of the electricity supply circuit when the operation is switched to the low power consumption mode by the mode switching unit.

3. The protector for the electricity supply circuit according to claim 1 , wherein the mode switching unit switches the controller to the low power consumption mode in response to the elapsed time being greater than the predetermined time and the estimated temperature of the electricity supply circuit being lower than the predetermined temperature occurring at a same time.